1. Technical Field of the Invention
This invention relates to electric power generation particularly on a small scale. This invention further relates to power conversion circuits that convert multi-phase electrical power generated by a permanent magnet generator into controlled electrical power that is fed to a local grid.
2. Description of Related Art
The deregulation of the electric utility industry has created a need for small-scale electrical power generation and the feeding of such power to the utility grid. Conventional small-scale electrical power generation systems typically utilize a diesel engine driven generator. Such generators typically have no control over how much power is delivered to the utility grid and, instead, feed the grid according to the load up to the maximum output power that the generator is capable of producing.
Recently, small scale turbines have been manufactured by companies to drive electrical generators. For example, Allied Signal manufactures a microturbine that is compact and highly efficient. Such turbines maximize efficiency if they can be run at a desired operating point.
As shown in FIG. 5, DC link converters for transforming electrical power are generally known. A DC link converter is essentially an AC/AC converter that utilizes a DC link. More particularly, a first voltage wave form V.sub.1 Sin.omega..sub.1 t is rectified into a DC voltage that is supplied to a DC link. The energy storage element (capacitor) located on this DC link provides more than filtering. The capacitor may also store any momentary mismatch in energy between the input and output power. This function is typically referred to as load balancing energy storage. The DC voltage on the DC bus may then be converted to a AC voltage by an inverter (labeled DC/AC converter in FIG. 5). The result is a desired AC wave form that may be expressed as V.sub.2 sin.omega..sub.2 t. Some uninterruptable power supplies (UPS) utilize a large DC bus capacitor C that is large enough to support the continued operation of the system in the event of a power failure.
There is a need for improved power conversion circuitry that is intended for electrical power generation on a small scale. More particularly, there is a need for generating electricity on a small scale wherein the electrical power that is generated is subject to a high degree of control such that the engine driving the generator can be operated at maximum efficiency while permitting withdrawal of a desired level of power from the generator when fed to a grid. Furthermore, there is a need for an apparatus that controls the supply of generated electrical power to the grid that permits a power level command to be entered by an operator wherein the apparatus automatically supplies such requested power at the correct line frequency and power factor, etc. to the utility grid.
Furthermore, conventional electrical generation systems do not permit starting of the engine by utilizing either power supplied from the grid or power from a secondary DC power source. Still further, there is no provision in the conventional art for simultaneously supplying power to a start inverter and supplying power to a grid.